Adults who reported ever having had a head injury and who were exposed to the herbicide paraquat had nearly a three-fold increased risk of developing Parkinson's disease, according to a survey published Monday in the journal Neurology.

Researchers at UCLA's Fielding School of Public Health surveyed more than 1,000 adults ages 35 and older who lived in central California. Some 357 of the participants were diagnosed with Parkinson's disease, a movement disorder characterized by tremors and loss of coordination.